It should be working. Are you running
emacs -nw because that might prevent it from working. Try pasting into another app instead of the one you're using for blog posting (browser?) such as
gedit and see if that works.
From the emacs manual:
26.1.2 Cut and Paste with Other Window Applications
To copy text to another windowing application, kill it or save it in
the kill ring. Then use the "paste" or "yank" command of the other
application to insert the text.
To copy text from another windowing application, use its "cut" or
"copy" command to select the text you want. Then yank it in Emacs with
When Emacs puts text into the kill ring, or rotates text to the
front of the kill ring, it sets the "primary selection" in the window
system. This is how other windowing applications can access the text.
On the X Window System, emacs also stores the text in the cut buffer,
but only if the text is short enough (the value of `x-cut-buffer-max'
specifies the maximum number of characters); putting long strings in
the cut buffer can be slow.
The commands to yank the first entry in the kill ring actually check
first for a primary selection in another program; after that, they check
for text in the cut buffer. If neither of those sources provides text
to yank, the kill ring contents are used.
The standard coding system for X Window System selections is
compound-text-with-extensions'. To specify another coding system for
selections, useC-x x' or `C-x X'. *Note Communication